This invention relates to the preparation of pre-coated ferrous-alloy components. More particularly, the present invention relates to the use of aluminum-containing organic, corrosion-inhibiting coatings to coat ferrous alloys used as aircraft structural components.
Aircraft manufacturers use a variety of different ferrous non-ferrous metals in the fabrication of aircraft components. Commonly assigned U.S. Pat. No. 5,614,037 discloses a method for pre-treating aluminum articles to obviate the use of wet-sealants and other coatings for protection against corrosion damage. Ferrous alloys such as carbon steels and aircraft-quality low-alloy steels, for example; Aermet 100, HY-TUF(trademark), 300M, H-11, HP9-4-30, 52100, 1095, 4130, 4135, 4140, 4330V, 4340, 6150, 8740, etc. are often used as structural aircraft components. Typically, these ferrous-alloy components which include fasteners, bearings, struts, etc., are protected from wear and corrosion by applying an overplate of cadmium alone or in combination with a chrome plate. These fasteners are often installed using wet-sealant. While this plated overcoat and/or use of wet-sealant protects the ferrous substrate from corrosion, such cadmium and chrome-plating and wet-sealant installation processes are time consuming, cumbersome, expensive and environmentally undesirable.
It would be extremely desirable to impart corrosion resistance to the ferrous substrate obviating the need for the chrome and cadmium-plating and/or wet-sealant installation processes. It would be further highly desirable to incorporate the coating cure step into an existing alloy fabricating process.
The present invention provides a method for preparing and treating ferrous-alloy aircraft structural components such as fasteners, fittings, hinges, bearings, gears, struts, etc., and the mechanical structures attached to these aforementioned components. The ferrous-alloy components of the present invention are heat-treated to impart good mechanical properties and also are protected by a cured, organic corrosion-resistant coating. The application of the organic coating obviates the need for cadmium or chrome-plating and/or use of wet-sealant during installation and does not adversely affect the desired final properties or performance of the component. To the contrary, the corrosion-resistant properties of the coated components are enhanced as compared to the properties of the plated and/or wet-sealant installed components.
One embodiment of the present invention relates to a method for providing a corrosion-resistant coating to a high-strength, ferrous-alloy aircraft structural component. An aircraft structural component made from a ferrous-alloy precursor is provided and subjected to an austenitizing treatment. The ferrous substrate is then quenched, followed by an optional xe2x80x9csnapxe2x80x9d heat-treat tempering step. The ferrous substrate is then coated with an aluminum-containing, curable organic coating having a non-volatile portion that is predominantly organic. The coating is curable at about the ferrous-alloy component""s heat-treatment tempering temperature, and is applied to the ferrous-alloy precursor prior to the final fall tempering step. The coating is flash cured (200xc2x0 F. for about 1-2 minutes). The coated, ferrous-alloy precursor is then tempered to concurrently 1) impart predetermined metallurgical properties or characteristics to the finished ferrous-alloy component, and 2) cure the organic, aluminum-containing coating.
In a further embodiment, the coated, ferrous-alloy component is formed, cold-worked or thread rolled into a completed or partially completed form and installed.
In a still further embodiment, the present invention relates to a further method for coating a high-strength, ferrous-alloy aircraft structural component with a corrosion-resistant coating. A high-strength aircraft structural component made from a ferrous-alloy precursor is provided and austenitized/normalized, followed by quenching. The component is then subjected to an optional xe2x80x9csnapxe2x80x9d temper step. The component is cold-worked or otherwise formed such as, by thread rolling, and then coated with an aluminum-containing, curable organic coating material having a non-volatile portion that is predominantly organic and is curable at about the ferrous-alloy material""s heat-treatment tempering temperature. The ferrous-alloy precursor is then subjected to the tempering temperature of from about 400xc2x0 F. to about 1150xc2x0 F. for a duration of from about 30 minutes to about 3.5 hours. The appropriate ranges depend on the specific ferrous-alloy being treated. Most preferably for the components of the present invention, the tempering temperature is about 825xc2x0 F. for about 1 hour. This tempering operation concurrently 1) imparts the desired metallurgical characteristics to the ferrous alloy material and 2) cures the coating.
These embodiments yield surprising and unexpected technical and cost advantages when used in conjunction with high-strength, ferrous-alloy aircraft structural components such as bearings, hinges, fittings, gears, struts, fasteners, etc. Through the use of the coating techniques of the present invention, the need to plate the ferrous alloys with cadmium or chrome and/or use wet-sealant in their installation for corrosion protection is obviated.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.